Soybean oil is more likely to induce diabetes and metabolic syndrome than pure fructose, according to a study conducted by researchers from the University of California-Riverside and published in the journal PLOS ONE.

"That was a surprise, given that most people think that unsaturated fatty acids are supposed to be healthy," lead author Poonamjot Deol said.

The study was designed to evaluate different types of fat in comparison with sugar to determine how they increase the risk of the cluster of symptoms known as metabolic syndrome. These symptoms -- central obesity, high fasting blood glucose, high triglycerides, high blood pressure, and low HDL ("good") cholesterol -- are associated with a significantly increased risk of diabetes and cardiovascular disease.

Saturated fats are the healthiest type

The researchers fed mice one of four diets. The first two diets derived 40 percent of their calories from fat to approximate the typical U.S. diet. In the first of these, all of the fat came from coconut oil, which is mostly saturated fat. In the second one, half the fat came from coconut oil and half came from soybean oil, which is mostly polyunsaturated fat. This second diet was similar to the amount of soybean oil consumed in the average U.S. diet.

The other two diets contained the same amount of calories and roughly the same volume of food, but some of the fat was replaced with fructose in levels similar to that consumed in the average U.S. diet.

The fructose diets were the highest in sugar, so the researchers believed that mice on these diets would add more body fat and develop more insulin resistance. Indeed, the mice on the fructose diets gained about 12 percent more weight than those on the saturated fat-heavy coconut oil diet.

However, the surprising finding was that mice on the soybean oil, fructose-free diet actually gained 9 percent more weight than the mice on the fructose diet and 25 percent more weight than mice on the coconut oil diet. The mice on the soybean oil diet also had fattier livers and higher insulin resistance than mice on the coconut oil or fructose diets.

"We've actually tested corn oil, and we found that it was also causing more obesity than coconut oil, but not as much as soybean oil. We haven't tested canola yet," Deol said.

GMO connection?

In order to help uncover the causes of any changes observed, the researchers also performed an in-depth analysis of gene expression and metabolism in all four groups. They found that soybean oil caused changes in the expressions of genes regulating not just how the liver processes fat but also how the body metabolizes various foreign chemicals, including drugs and environmental toxins.

Another possible cause for the observed effects of soybean and corn oil -- although not one mentioned by the researchers -- is the genetic modification of those foods. Fully 89 percent of U.S. corn acreage and 94 percent of U.S. soy acreage is now modified to resist various herbicides, primarily Roundup (glyphosate). Studies have shown that genetically modified organisms (GMOs) can have metabolic effects; in addition, GMOs are sprayed with much higher levels of herbicides, leading to higher levels of endocrine-disrupting herbicide residue on foods.

For those hoping to cut soybean oil (GMO or not) out of their diets, the best thing to do is cut back on processed and restaurant foods. That's because soybean oil has become ubiquitous in the U.S. food supply; it now accounts for 60 percent of U.S. oil consumption.